The aims of the present study were to show the distribution of individual myosin light chain (MyLC) isoforms in fast-twitch (FT) and slowtwitch (ST) muscles and between FT muscles in order to find differences between MyLC isoforms in these muscles, to identify similarities with the distribution of myosin heavy chain (MyHC) isoforms and to investigate changes in these relations during adaptation to endurance and resistance training. Male Wistar strain rats were used in this study. One-dimensional electrophoresis was used for separation of MyHC and MyLC isoforms and two-dimensional electrophoresis was used for identification of MyLC different isoforms. A difference in the relative content of MyLC isoforms between FT muscles exists only in the case of MyLC 1slow and 2slow isoforms. Differences in the relative content of MyHC between FT muscles are considerably larger than differences in the MyLC isoforms. MyHC and MyLC isoforms both participate in the remodelling of contractile proteins during exercise training. In conclusion: The present study shows some discrepancy between the modulation of MyHC and MyLC isoforms in muscles with different oxidative potential during adaptation to endurance and resistance training. In ST muscles, there is full agreement between the increase in the relative content of MyHC IIa isoform and MyLC 2fast and 3fast isoforms during resistance training without significant changes during endurance training. The ratio of MyLC 3 and MyLC 2 isoforms increases during both types of exercise training, but it is two times higher during resistance training.
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